Sweeney found Tracy Monteiro, 32, lying at the end of his driveway minutes before dispatchers received the first 911 call from the area.

"That definitely helps out a lot, especially at that hour of the morning. It was invaluable," said New Bedford police Detective Capt. Steven Vicente.

"By the time someone wakes up, figures out what they heard, goes to the telephone, calls in to dispatch, several minutes have gone by. In this situation, information was instantaneously sent to the cruisers."

The city installed ShotSpotter, a system of acoustic sensors, earlier this year for about $950,000. The sensors are designed to detect and pinpoint gunfire so police dispatchers can get officers to the scene quickly.

However, as of Monday, detectives were still trying to piece together where Monteiro might have gone or whom he might have spoken with in the hours before neighbors heard five to six shots outside.

Monteiro's live-in girlfriend said she last saw him at 11:30 p.m. Saturday when she left a baby shower the couple had attended at a North End banquet hall. She said Monteiro planned to return to the shower, then go out with friends.

Monteiro's girlfriend — who requested anonymity — told The Standard-Times Sunday that Monteiro was not involved with drugs or guns and said he was not violent.

Authorities did not say Monday if they had identified possible suspects. Gregg Miliote, spokesman for the Bristol County District Attorney's Office, declined to comment, citing the ongoing investigation.

Monteiro's homicide marked the city's third of 2011 and the second this month. On Nov. 9, police found the body of Mike Duarte, 36, inside a single-family home at 1058 Churchill St. Authorities have not disclosed the cause of death.

The main suspect in Duarte's murder, Thomas Gardner, 35, of New Bedford, was arrested Nov. 9 in Connecticut after driving Duarte's car, which had been reported stolen when Duarte went missing four days earlier.

Gardner — the last person Duarte is known to have arranged to meet before his death and in whose former house the victim's body was found — is awaiting extradition to Massachusetts to be arraigned on a stolen motor vehicle charge. He has not been charged with murder.